Chen Zhuo, Valentine Richard L
Civil and Environmental Engineering, 4105 Seamans Center for the Engineering Arts and Sciences, The University of Iowa, Iowa City, Iowa 52242-1527, USA.
Environ Sci Technol. 2006 Dec 1;40(23):7290-7. doi: 10.1021/es0605319.
This paper presents mechanistic studies on the formation of NDMA, a newly identified chloramination disinfection byproduct, from reactions of monochloramine with natural organic matter. A kinetic model was developed to validate proposed reactions and to predict NDMA formation in chloraminated water during the time frame of 1-5 days. This involved incorporating NDMA formation reactions into an established comprehensive model describing the oxidation of humic-type natural organic matter by monochloramine. A rate-limiting step involving the oxidation of NOM is theorized to control the rate of NDMA formation which is assumed to be proportional to the rate of NOM oxidized by monochloramine. The applicability of the model to describe NDMA formation in the presence of three NOM sources over a wide range in water quality (i.e., pH, DOC, and ammonia concentrations) was evaluated. Results show that with accurate measurement of monochloramine demand for a specific supply, NDMA formation could be modeled over an extended range of experimental conditions by considering a single NOM source-specific value of thetaNDMA, a stoichiometric coefficient relating the amount of NDMA produced to the amount of NOM oxidized, and several kinetic parameters describing NOM oxidation. Furthermore, the oxidation of NOM is the rate-limiting step governing NDMA formation. This suggests that NDMA formation over a 1-5 day time frame may be estimated from information on the chloramine or free chlorine demand of the NOM and the source-specific linear relationship between this demand and NDMA formation. Although the proposed model has not yet been validated for shorter time periods that may better characterize the residence time in some distribution systems, the improved understanding of the important reactions governing NDMA formation and the resulting model should benefit the water treatment industry as a tool in developing strategies that minimize NDMA formation.
本文介绍了关于新发现的氯胺消毒副产物N-亚硝基二甲胺（NDMA）由一氯胺与天然有机物反应形成的机理研究。开发了一个动力学模型，以验证所提出的反应，并预测在1至5天的时间范围内加氯胺水中NDMA的形成。这涉及将NDMA形成反应纳入一个既定的综合模型，该模型描述了一氯胺对腐殖型天然有机物的氧化作用。理论上，一个涉及天然有机物氧化的限速步骤控制着NDMA的形成速率，假定该速率与被一氯胺氧化的天然有机物的速率成正比。评估了该模型在广泛水质范围（即pH值、溶解性有机碳和氨浓度）下，描述三种天然有机物来源存在时NDMA形成的适用性。结果表明，通过准确测量特定供应下的一氯胺需求量，考虑单一天然有机物来源特定的θNDMA值（一个将产生的NDMA量与被氧化的天然有机物量相关联的化学计量系数）以及几个描述天然有机物氧化的动力学参数，可在扩展的实验条件范围内对NDMA形成进行建模。此外，天然有机物的氧化是控制NDMA形成的限速步骤。这表明，在1至5天的时间范围内，NDMA的形成可根据天然有机物对氯胺或游离氯的需求量以及该需求量与NDMA形成之间的来源特定线性关系来估算。尽管所提出的模型尚未针对可能更好地表征某些配水系统停留时间的较短时间段进行验证，但对控制NDMA形成的重要反应的进一步理解以及由此产生的模型，应会使水处理行业受益，成为制定将NDMA形成降至最低的策略的工具。
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